Basic chemistry

What is radioactivity in simple words?

Radioactivity definition?


Radioactivity definition:

Radioactivity definition is as a physical phenomenon naturally present in the Universe. It is due to unstable atomic nuclei which disintegrate and give off various more or less pathogenic radiations. 

Unisciel and the University of Lille 1 enlighten us, with the Kezako program, on the risks and effects of this radiation.

The radioactivity is primarily a natural phenomenon .

Natural radioactivity:

Indeed, some atoms are unstable: they are called ” radionuclides “. They have the property of disintegrating spontaneously, to give another element, by emitting particles ( electrons , neutrons , etc.) or electromagnetic radiation. We then say that they are “radioactive”.

Note that radioactivity changes the composition of the atomic nucleus and, therefore, the nature of the atom.

Artificial radioactivity:

Radioactivity can also have an artificial origin (medical examination, therapy , discharges from nuclear installations, etc.) when the same effect is obtained by bombarding the nuclei of atoms .

Alpha, beta and gamma decays:Radioactivity definition

There are three main types of decays:

  • Alpha (α) decay results in the emission of α radiation . The atom loses protons and neutrons. There is emission of a helium nucleus . The periods of α decays are often long.
  • Disintegration beta (β) results in the emission of a β radiation. A neutron turns into a proton or  vice versa . Most often there is emission of an electron and an antineutrino or, sometimes, emission of a positron and a neutrino . The radioactive periods of β decays are shorter, sometimes even very short.
  • Gamma radiation (γ) corresponds to the emission of energetic photons .

Radioactivity and health:

For the French population, the maximum dose of artificial radiation (excluding medical applications ) is set at 1 millisievert per year (mSv / year); the average natural dose is of the order of 4.5 mSv / year. Ionizing radiation emitted during radioactive decays can have effects on health. They depend :

  • the radiation dose ;
  • the nature of the radiation:
    • the penetrating power of α radiation is low. It can be stopped by a sheet of paper  ;
    • When an atom emits an electron (β radiation), it can be stopped by a few millimeters of aluminum .
    • When an atom emits a positron (β radiation), it annihilates an electron, which produces γ rays.
    • An α or β decay is generally followed by a γ emission. It takes about a yard of lead or concrete to stop it.
  • exhibition terms:
    • we speak of irradiation when the exposure is external;
    • we speak of  contamination when the exposure is internal ( ingestion of contaminated food, for example).
  • of the exposed organ or tissue.

Read more:

Radiation basics?

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